Lubricant compositions

ABSTRACT

DIESTERS OF 1,4,5,6,7,7-HEXACHLOROBICYCLO (2.2.1)-HEPT-5ENE-2,3-DICARBOXYLIC ACID ARE LUBRICANT ADDITIVES FOR IMPROVING THE PERFORMANCE OF SILICONE OIL AND GREASE.

United States Patent 3,759,827 LUBRICANT COMPOSITIONS Eugene D. Groenhof, Midland, and Terence J. Swihart,

Essexville, Mich., assignors to Dow Corning Corporation, Midland, Mich. No Drawing. Filed Sept. 29, 1970, Ser. No. 76,631 Int. Cl. Cm 3/24, 3/46, 7/50 U.S. Cl. 252--29 10 Claims ABSTRACT OF THE DISCLOSURE Diesters of 1,4,5, 6,7,7-hexachlorobicyc1o 2.2. 1 -hept-5- ene-2,3-dicarboxylic acid are lubricant additives for improving the performance of silicone oil and grease.

This invention relates to improved lubricating compositions and more particularly to silicone lubricants having high load-carrying capacity.

Because of their high temperature stability and low pour points silicone fluids find wide application as lubricants. As discussed by Noll in Chapter 9 of Chemistry and Technology of Silicones, copyright 1968 by Academic Press, silicone fluids cannot be considered general lubricating oils because of their minimal lubrication of steel on steel, especially when sliding friction is involved. Various additives, such as chlorinated biphenyls, brominated fatty acids and esters of phosphoric acid, have been proposed for improving the lubricating characteristics of polysiloxanes. While certain additives do enhance the lubrication properties at normal temperatures, the additive effect disappears at extreme high and low temperatures because of inadequate heat stability or because of insolubility at the lower temperatures.

One specific class of lube additives is based on the reaction product of chlorendic acid with various organic compounds such as chlorinated alcohols, lauryl mercaptan and alkanol amines. This class or additives has been recommended for use in both natural lubricants, e.g.: mineral oil, and synthetic lubricants, e.g.: polyesterssee U.S. Pats. 3,426,062, 3,388,191, and 3,234,132. Calcium salts of chlorendic acid are disclosed specifically as lube additives for silicones in U.S. Pat. 3,223,632 which describes the additive as being insoluble, having principal utility as a thickening agent in silicone grease.

By practice of the present invention, wherein alkylesters of chlorendic acid are utilized as lube additives for silicone fluids, there is obtained additive solubility and stability over a major portion of the operational temperature range of the lubricant. Additionally, steel on steel lubricating characteristics are imparted to the silicone.

Thus, it is an object of the present invention to provide improved lubricant compositions.

Another object of the invention is to provide organopolysiloxanes having steel on steel lubricating properties.

These and other objects of the invention will be apparent to one skilled in the art upon consideration of the following disclosure and claims.

In accordance with the present invention, there are provided lubricant compositions comprising a major amount of a liquid diorganosiloxane and a small amount, willcient to improve the load-carrying characteristics of the liquid siloxane, of a diester of the formula in which R is an alkyl radical of from 4 to 8 inclusive carbon atoms. Within the described carbon atom limita- 3,759,827 Patented Sept. 18, 1973 ice tion the R radical can be a straight or branched alkyl. Thus, the use of dibutylchlorendate, dihexylchlorendate, dioctylchlorendate, and di-Z-ethylhexylchlorendate and the like are contemplated in the practice of the invention.

The above described diester is readily formed by reacting the carboxyl groups of chlorendic acid with alcohols having from 4 to 8 carbon atoms in the molecule. Chlorendic acid, otherwise identified as l,4,5,6,7,7-hexachlorobicyclo(2.2.1)-hept-5-ene-2,3-dicarboxylic acid, is prepared by the Diels-Alder addition of the corresponding chlorinated cyclopentadiene and maleic anhydride. Chlorendic acid is commercially available from the Velsicol Chemical Corporation, Chicago, Ill.

The silicone fluids utilized in the practice of the invention are described as liquid diorganopolysiloxanes and can be represented by the general formula:

[i' i" R'S]i0)Si-R D in which each R is selected from the group consisting of the hydrogen atom, alkyl and halogenated alkyl radicals, aryl and halogenated aryl radicals, alkaryl, aralkyl and halogenated derivates thereof. The depicted polymers are triorganosilyl-endblocked the all: C F 3CHgCHg(CH 213i 0 Siloxanes having R substituents of less than 18 carbon atoms are preferred. Most preferred in the practice of the invention are dimethylpolysiloxanes,

and phenylmethylsiloxane copolymers or homopolymers. The physical characteristics of these siloxanes are discussed in detail by Gunderson and Hart in Chapter 7 of Synthetic Lubricants copyright 1962 by Reinhold Publishing Corporation. The silicone fluids have a viscosity of from 0.65- to over 1,000,000 cs. (centistokes) when measured at 77 F. Particularly preferred are those liquid diorganopolysiloxanes having a viscosity in the range of about 20 to 1000 cs. at 77 C. If desired, blends of differviscosity siloxane liquids can be utilized.

The lubricant compositions of the invention are prepared by blending the above-described components, the diester being soluble in the siloxane. This solubility has been observed at temperatures as low as -20 F. in concentrations of 5 weight percent in polydimethylsiloxane. The amount of diester additive is sufficient to improve the load-carrying characteristics to the desired degree. This amount will vary with the nature of the organosiloxane and its application, but it will generally be in the range of from 1 to 10 weight percent, based on the weight of the liquid diorganopolysiloxane.

Other additives can be utilized in the above lubricating compositions to improve specific properties without departing from the scope of the invention. Thus, the lubricating compositions of the invention may optionally contain corrosion inhibitors, extreme pressure agents, antioxidants, dyes and the like. These additives are generally present in no more than 5-10 weight percent based on the weight of the lubricant compositions.

In addition to the use of known additives, the invention contemplates the use of thickening agents with the lubricant compositions to produce grease formulations having improved load-carrying characteristics. Any suitable thickening agent can be formulated with the diorganopolysiloxane-diester lubricant to produce grease compositions. Suitable thickening agents include fatty acid soaps, carbon black, silica, clay, copper phthalocyanine, ammeline, indantherene blue, aryl-substituted ureas, polytetrafluoroethylene and the like. Nitrogen-containing thickening agents, such as aromatic ureas, aromatic di-ureas, aromatic amides, aromatic di-amides, abietyl di-urea, cyanuramide and eyanourodiamide, are especially suitable in the formulation of high temperature greases. These thickeners are well-known in the art, being described in detail in US. Pat. 3,278,435. The lithium soaps of high molecular weight carboxylic acids, for example lithium stearate, are preferred thickeners for grease compositions designed for use in less severe temperature environments.

The thickening agent will generally be present in an amount from about to 60 weight percent of the total grease composition, depending upon the consistency desired. Grease compositions containing from 20 to 40 weight percent thickener are preferred because of their varied applications. The grease compositions of the invention can be prepared by mixing the thickener and any other components with the lubricant composition on a three-roll mill, tcol'lodial mill or the like. Other conventional methods can be used to prepare the grease so long as one obtains an intimate mixture of the components.

The following examples are illustrative and not to be construed as limiting of the present invention which is delineated in the claims. In the examples, lubricity characteristics were determined by means of 4-Ball test and LFW-l test. The 4-Ball test is conducted on a Roxanna weak testing machine and a Az-inch diameter steel ball is roated against three stationary /z-inch diameter steel balls at a rate of 1200 r.p.m. for one hour at a temperature of 167 F. under loads ranging from 10 to 40 kilograms. At the end of the one hour, the length and width of the scar formed on each stationary ball is measured and the average of the six measurements is taken as the Wear scar diameter. The smaller the wear scar, the better the lubricant. Wear scars for certain grease formulations were also determined on the Alpha LEW-1 test machine in the oscillating mode, using a standard steel ring on a R 30 steel block at a 10 arc and 75 cycles per minute. The wear scar resulting from the oscillations is measured after 500 cycles at 150 pounds load.

EXAMPLE 1 Suflicient dibutylchlorendate was blended with trimethylsilyl-endblocked dimethylpolysiloxane to form a 10 Weight percent solution of the diester in the siloxane. The fluid dimethylpolysiloxane had a viscosity of 350 cs. When measured at 77 F. The dibutylchlorendate-siloxane solution was stable at room temperature. This lubricant composition gave a 4-Ball wear scar diameter of 0.73 mm. under 40 kg. load and 0.57 mm. under 10 kg. load. The use of the fluid siloxane without any additive as a lubricant results in a wear scar of 2.33 mm. This data demonstrates that the diester additive does impart steel on steel lubricating properties to dimethylpolysiloxane.

EXAMPLE 2 A grease formulation contains a 90.7 weight percent of liquid diorganopolysiloxane, 0.7 weight percent dye and 8.6 weight percent of lithium stearate (thickener) was prepared by the in situ reaction of 1.2 weight percent lithium hydroxide with 7.4 weight percent stearic acid in the siloxane vehicle. The liquid diorganopolysiloxane consisted of 84.3 mol percent (CI-I SiO units, 9.8 mol percent C H (CH )SiO units and 5.9 mol percent units and had a viscosity of 100 cs. at 77 F. A portion of this grease was mixed with suflicient dibutylchlorendate 4 to form a grease composition containing 5 weight percent of the additive. When tested by the 4-Ball method at 1200 r.p.m. for one hour at room temperature under a load of 5 kilograms the additive-containing grease resulted in a wear scar of 2.4 mm. as compared to a wear scar of 3.0 mm. resulting from use of the unmodified grease.

A second grease formulation (Grease No. 2) containing 64 weight percent of trimethylsilyl-endblocked 3,3,3- trifluoropropylrnethylpolysiloxane (1000 cs.), 26 weight percent of powdered polytetrafluoroethylene resin and 10 weight percent powdered tetrafluoroethylene-hexafluoropropylene copolymer was prepared by milling of the components. A portion of this grease was mixed with sufficient dibutylchlorendate to form a grease composition containing 5 weight percent of the additive. This grease and the above-described lithium stearate thickened grease were tested by means of the described LFW-1 test. Results are listed below:

LFW-l Grease composition: wear scar (mm.) Grease No. l-unmodified 2.7 Grease No. l 5 weight percent dibutylchlorendate 1.6 Grease No. 2unmodified 1.8 Grease No. 2 5 weight percent dibutylchlorendate 1.6

These data demonstrate the superior lubrication propcries of grease compositions prepared in accordance with the invention. It is to be noted the lubrication of the fluorosilicone grease (No. 2) are relatively good to start with, yet are enhanced by addition of the dibutylchlorendate.

EXAMPLE 3 Suflicient di-Z-ethylhexylchlorendate was blended with copolymeric siloxane to form a 5 weight percent solution of the diester in the disiloxane. The liquid siloxane consisted of 57 mol percent C H (CH )SiO units, 30.5 mol percent (CH SiO and 12.5 mol percent (CH SiO units and had a viscosity of 135 cs. at 77 F. This lubricant composition gave a 4-Ball wear scar diameter of 2.1 mm. under a 10 kg. load as compared to a wear scar of 2.53 mm. under 10 kg. obtained from the unmodified fluid siloxane.

EXAMPLE 4 For purposes of comparison various additives, including the diesters of the invention, were used in combination with trimethylsilyl-endblocked dimethylpolysiloxane having a viscosity of 350 cs. The additives were mixed with portions of the liquid siloxane in amounts sufficient to provide 5 weight percent concentrations of the particular lube addtives. The various additive-siloxane mixtures were tested by the 4-Ball method under 40 kg. load. The coefficient of friction for each lubricant composition was also determined. Descriptions of the additives and test results are tabulated below:

Coetfi- 4-bal1 cient of wear seat friction Additive (mm.) f are 1... None 2.33 0.3 2- Dibutylchlorendate 0. 87 0. 065 3. Di-2-ethlhexylchlorendate.-- 0. 0. 058 4. Chlorinated diphenyl conta g 54 w ht percent chlorine. 1. 2 0. 20 5- Chlorinated diphenyl containing 62 weight percent chlorine. 1. 6 0. 24 6 Imide product from reaction of alkylamine with 5, 6, 7, 8, 9, Q-hexachloro-l,2,3,4,4a,5,8, 8a-octahydro-5,8-methano-2,3-naphtholenedicarboxylic acid. 1. 9 0.25 7- N-n-butyl chlorondie imide 1. 5 0. 19 8. Dicalcium chlorendate d 1. 7 0. 26

' Qommercially available from Monsanto Company, St. Louis, Missoun.

b Available from Universal Oil Products Company, Des Plaines, Illinois and described in U.S. Patent 3,208,039.

" Described in U.S. Patent; 2,795,589.

4 The reaction product of ehlorcndie anhydride and calcium hydroxide prepare by the method described in Example 1 of [7.8. Patent 3,223,632.

Additives 6 through 8 were insoluble in the liquid siloxane at the stated concentration. The cloud point of dibutylchlorendate-containing solution was 20 F. as compared to +45 F. for the solution containing additive No. 4, and +65 F. for the solution containing additive No. 5. Thus, the additive-containing siloxanes of the invention are the only species of the above additive-containing lubricants which would not be subject to precipitation or phase separation during shipping and storage.

The wear scar values and coeflicients of friction demonstrate the superior lubrication obtained by practice of the invention. The dibutylchlorendate additive is shown to give only one-half the wear resulting from use of dicalcium chlorendate, which is specifically recommended for use in silicone lubricants.

Reasonable modification and variation are within the scope of the invention which is directed to novel lubricant compositions.

That which is claimed is:

1. A lubricant composition comprising a major amount of a liquid diorganopolysiloxane and a small amount, sufficient to improve the load-carrying characteristics of the liquid siloxane, of a diester of the formula CHC0R in which R is an alkyl radical of from 4 to 8 inclusive carbon atoms.

2. A lubricating composition in accordance with claim 1 wherein the diester is present in an amount in the range of from 1 to 10 percent by weight, based on the weight of liquid siloxane.

3. A lubricant composition in accordance with claim 1 wherein the diester R is a butyl radical.

4. A lubricant composition in accordance with claim 3 wherein the liquid polydiorganosil-oxane is dimethylpolysiloxane having a viscosity in the range of 20 to 1000 cs. as measured at 77 F.

5. A lubricant composition in accordance with claim 3 wherein the liquid diorganopolysiloxane contains phenylmethylsiloxane units.

6. A lubricant composition in accordance With claim 5 wherein the siloxane is phenylmethylpolysiloxane.

7. A lubricating composition in accordance with claim 1 containing suflicient thickening agent to form a grease.

8. A grease composition in accordance with claim 7 wherein the thickening agent is present in an amount in the range of about 10 to Weight percent, based on the total weight of the composition.

9. The grease composition of claim 8 wherein the thickening agent is lithium stearate.

10. The grease composition of claim 7 wherein the thickening agent is carbon black.

References Cited UNITED STATES PATENTS 3,158,575 11/1964 Jordan et al. 25254.6 3,208,939 9/1965 Lotos et al. 25229 2,971,913 2/1961 David et a1. 25254.6 2,771,423 11/1956 Dorinson 25254.6 2,890,170 6/1959 Ragborg 252--54.6 3,048,540 8/1962 Eastman et al. 25254.6

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 

